TOKYO (Reuters) - Japan has drafted new guidelines that would reverse a decades-old ban on weapons exports, a source with knowledge of the matter said on Sunday, a move that could further strain ties with neighbors China and South Korea.

Tokyo has been reviewing the self-imposed export ban under Prime Minister Shinzo Abe's new security strategy, aimed at bolstering the self-reliance of the military.

Serving as prime minister for a rare second time and enjoying solid public approval, Abe says Japan needs a stronger military to cope with what he calls an increasingly threatening security environment, with a more militarily assertive China and unpredictable North Korea.

The proposed revision could draw criticism from China and South Korea, where resentment over Japan's wartime aggression still runs deep. Beijing and Seoul also have long-running territorial disputes with Tokyo over different sets of islets.

Japan drew up the "three principles" on arms exports in 1967, banning sales to countries with communist governments or those involved in international conflicts or subject to United Nations sanctions.

But the rules over time became tantamount to a blanket ban on exports - with some exceptions - and on the development and production of weapons with countries other than the United States.

Under the new guidelines, arms exports would be approved upon "rigorous review" if they were to serve peaceful missions or if joint development of a weapon was deemed to enhance national security, the source told Reuters.

The draft principles omit the ban of exports to governments that are involved in international conflicts, a move that Japanese daily Asahi Shimbun said on Sunday was aimed at paving the way for more sales to countries like Israel, which last year bought Lockheed Martin's F-35 jets with Japan-made components.

"It's not necessarily aimed at boosting exports so much as clarifying the types of cases in which exports were previously allowed under exceptional circumstances," the source said, declining to be identified because the draft is not public.

The Liberal Democratic Party-led government hopes to agree the revision with its more dovish coalition partner, the New Komeito Party, and approve the change as early as next month, the source said.

The current export ban has traditionally kept Japanese defense contractors, such as Mitsubishi Heavy Industries Ltd, Kawasaki Heavy Industries Ltd and IHI Corp, from taking part in international weapons development programs, making it difficult for them to stay abreast of technological development and drive down costs.